In computer networking, a single layer-2 network may be partitioned to create multiple distinct broadcast domains, which are mutually isolated so that packets can only pass between them via one or more routers. Such a domain is generally referred to as a virtual local area network (VLAN). This is usually achieved on switching or routing network devices. Some devices may support VLAN by partitioning on a port level; other devices can mark packets through tagging so that a single interconnect (trunk port) may be used to transport data for various VLANs. A VLAN has the same attributes as a physical local area network (LAN), but it allows for client devices to be grouped together more easily even if they are connected to the same network switch. VLAN membership can be configured through software. Unlike physically separate networks, VLANs share bandwidth, so VLAN trunks may require aggregated links and/or quality of service prioritization.
The Dynamic Host Configuration Protocol (DHCP) generally refers to a standardized networking protocol used on Internet Protocol (IP) networks for dynamically distributing network configuration parameters, such as IP addresses for interfaces and services. With DHCP, client devices of a network request IP addresses and networking parameters automatically from a DHCP server, reducing the need for a network administrator or a user to configure these settings manually.
In a wireless local area network (WLAN), when a client device belonging to a particular VLAN requests an IP address, a network control device will forward the request to the DHCP server corresponding to the particular VLAN. The DHCP server will then assign an IP address to lease to the client device. Specifically, the DHCP server can maintain an address pool for the particular VLAN. Upon receiving the DHCP request, the DHCP server assigns an available IP address in the address pool for the particular VLAN to the client device with a predetermined period of time, and marks the assigned IP address as unavailable. If the client device fails to renew the IP address, the DHCP server will release the assigned IP address as an available IP address to the address pool for the particular VLAN. The client device may fail to renew the IP address, for example, after the client device disconnects with the WLAN. In such scenarios, the IP address will be reserved for the predetermined period of time until the lease period expires. The DHCP server will then reuse the IP address by including the IP address in the DHCP available address pool, and thus making it available for other client devices.
Many types of public facing network environments, such as, airports, super markets, hospitals, etc., usually have a visitor population that is very dynamic. For example, a significant portion of the WLAN client devices may only be connected to the network for a short time, and would probably not re-connect again for a long time. Another portion of the WLAN client devices may stay connected for a considerable time interval. Note that, even if a client device, which is previously assigned an IP address by the DHCP server, is disconnected and moves away from the WLAN, the DHCP server still cannot reuse the Internet Protocol (IP) address until the DHCP lease expires. Therefore, when a large number of client devices connect to the WLAN for a short time and then leave the WLAN, the DHCP pool exhaustion would occur rather quickly.
An existing solution is to use a short DHCP lease period to reduce the likelihood of DHCP pool exhaustion. However, a short DHCP lease period would require client devices which connect to the WLAN for longer periods continuously to renew their DHCP leases, which is inconvenient and inefficient for such client devices.